1. Field of the Invention
The present invention relates generally to apparatus for loading spare wheels on vehicle bodies, and more particularly, to a spare wheel loading apparatus for loading automatically spare wheels on spare wheel holding portions provided in vehicle bodies which are supported and transported successively by carriers mounted on a vehicle body carrying conveyor.
2. Description of the Prior Art
In a vehicle body assembly line, a vehicle body is supported and transported by a carrier, such as a hanger, mounted on a vehicle body carrying conveyor of, for example, the trolley type to be subjected to equipments of various parts and components. Although work for loading a spare wheel on a spare wheel holding portion provided in, for example, a trunk of the vehicle body in the vehicle body assembly line has been previously in reliance on manual labor, there has been recently proposed, for reduction of labor, such technology as to load automatically spare wheels on vehicle bodies transported successively by the vehicle body carrying conveyor in the vehicle body assembly line.
One of previously proposed spare wheel loading apparatus for loading automatically spare wheels on vehicle bodies is disclosed in Japanese patent application published before examination under publication No. 50/60775. This previously proposed spare wheel loading apparatus is composed of a robot having an arm for catching a spare wheel and move the same into each of vehicle bodies in process of transportation by a vehicle body carrying conveyor, a servo valve disposed on a pressure oil path to be engaged temporarily with each of hangers mounted on the vehicle body carrying conveyor for supporting the vehicle bodies and operative to open the pressure oil path on the occasion of engagement with one of the hangers conveying the vehicle bodies, a first cylinder having first and second oil chambers and operative to cause the servo valve to move together with the hanger engaging therewith when a pressure oil is supplied through the servo valve to the first oil chamber, and a second cylinder supplied with the pressure oil discharged from the second oil chamber of the first cylinder for rotating the arm of the robot.
In the case where the spare wheels are loaded automatically on the vehicle bodies by the spare wheel loading apparatus proposed previously as mentioned above, however, it is very difficult to cause the speed of rotation of the arm of the robot to coincide with the speed of movement of the vehicle body which is transported linearly and the rotation of the arm of the robot is apt to get behind to the vehicle body transported. This results in that a position to which the spare wheel is removed from the arm of the robot is apt to be deviated from a spare wheel holding portion provided in the vehicle body and therefore it is feared that a situation wherein the spare wheel is not loaded properly on the vehicle body arises.
In order to avoid such problems as mentioned above, it is considered to provide an improved spare wheel loading apparatus which includes a robot having an arm operating with a predetermined working path and at a predetermined working speed to load a spare wheel on each of vehicle bodies transported by a vehicle body carrying conveyor, a robot moving device for shifting the robot along a direction of transportation of the vehicle body, and a speed sensor for detecting a speed of transportation of the vehicle body based on a signal obtained from a driving device, such as a motor, for driving the vehicle body carrying conveyor, and in which the robot moving device is driven to shift the robot in accordance with the speed of transportation of the vehicle body detected by the speed sensor, so that the robot is caused to shift along the direction of transportation of the vehicle body at the same moving speed as the vehicle body and operate to load the spare wheel on a spare wheel holding portion provided in the vehicle body in process of transportation. With such an improved spare wheel loading apparatus, since the robot having the arm which operates to load the spare wheel on the vehicle body transported by the vehicle body carrying conveyor is moved substantially together with the vehicle body and therefore the spare wheel can be loaded correctly on the spare wheel holding portion provided in the vehicle body.
However, in the above mentioned improved spare wheel loading apparatus constituted as described above, in actual, the speed of transportation of the vehicle body detected by the speed sensor is ready to include errors resulting from slips between the vehicle body carrying conveyor and the driving device for driving the vehicle body carrying conveyor, aged deterioration of the vehicle body carrying conveyor, or other undesirable but unavoidable causes. In the case where the speed of transportation of the vehicle body detected by the speed sensor includes such errors, a relative positional deviation arises between the vehicle body transported by the vehicle body carrying conveyor and the arm of robot, so that the spare wheel is prevented from being loaded properly on the spare wheel holding portion provided in the vehicle body. Especially, in the event of the relative positional deviation brought about on a large scale, it is feared that the vehicle body transported by the vehicle body carrying conveyor and the arm of robot interfere with each other.